In general, devices for running on a flat tire are devices which serve, when placed inside a tubeless pneumatic tire mounted on a wheel rim, to enable vehicles whose wheels are fitted therewith to continue to run in satisfactory manner in the event of partial or total loss of inflation pressure in the tire. One application for such devices is to be fitted to the wheels of vehicles that are required to travel in zones where traffic is difficult or dangerous and in which a degree of mobility must be conserved under all circumstances, regardless of whether the loss of tire pressure is accidental or has been provoked deliberately.
The conditions that such devices need to satisfy are both severe and contradictory. In the event of a puncture or even of a partial loss of inflation pressure in a tire, it is important:
to prevent the beads of the tire coming off their seats on the rim, regardless of whether the rim is of the flat type, is demountable or not, or is a well-based rim or a drop-center rim;
to limit the collapse of the tire;
to prevent the tire tread being damaged too quickly by pinching where it comes into contact with the device; and
to conserve the best possible shock-absorbing characteristics for the wheels.
A ring device of the type specified above is described in document FR-A-2 654 989 where the ring is constituted by an assembly of a plurality of arcuate sectors provided with coupling means at each of their ends. The ring is made of a composite material based on a reinforced thermoplastic resin, the lip of the abutment for holding the bead of the tire is integral with each of the ring sectors, and the wedge for holding the other bead of the tire is made of elastomer and is fixed on the sectors.
In general, such a ring device for running on a flat tire suffers from two types of drawbacks in particular. The first type of drawbacks lies in the use of a material that is very rigid and that may cause the tire to puncture in the event of a frontal shock, e.g. against a curb stone, thereby causing the tire cover to come into contact with the ring. Given the way the device is mounted inside the tire, this rigidity of its material also implies that the ring must be made up of a plurality of sectors. The second type of drawbacks lies in assembly and disassembly operations which are lengthy, which require the use of qualified operatives, and which imply the use of special tools. Such a device is also expensive.